Insulation sheet fixing structure and method for manufacturing insulation sheet fixing structure

Abstract

To provide a fixing structure of an insulating sheet in which the number of components and the number of assembling man-hours are small, and reduction in fixing force due to heat, vibration or the like hardly occurs, and to provide a manufacturing method capable of easily manufacturing the fixing structure of the insulating sheet.SOLUTION: A fixing structure of an insulating sheet according to the present invention includes an insulating sheet made of a resin material, and a protected object fixed by the insulating sheet and insulated and protected by the insulating sheet, wherein the protected object includes a base body having a first surface and a second surface having a front-back relationship with each other, and a through hole penetrating the base body from the first surface to the second surface, the insulating sheet includes a flat plate portion extending in a flat plate shape along the first surface, an expansion portion located outside the through-hole of the second surface, and a coupling portion that couples the flat plate portion and the expansion portion and is inserted into the through-hole.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fixing structure for an insulating sheet and a method for manufacturing the fixing structure for an insulating sheet. [Background technology]

[0002] 2. Description of the Related Art Electronic components, such as power elements, to which high voltages are applied, need to be sufficiently insulated from surrounding components.

[0003] For example, Patent Document 1 discloses a power element heat dissipation structure including a printed wiring board, a metal thin plate, a power element, heat dissipation components such as a heat sink, and an insulating sheet. In this power element heat dissipation structure, the insulating sheet is sandwiched between the power element and the metal thin plate. Holes for passing screws are formed in the insulating sheet, and when the power element is screwed to the metal thin plate, the insulating sheet is also screwed and fixed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-187426 Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration described in Patent Document 1, the insulating sheet needs to be fastened with screws, which increases the number of assembly steps and parts required for the power element heat dissipation structure. In addition, the insulating sheet is used in a state where it is fixed to a member that requires insulating protection, but this increases the number of parts in the fixing structure and the resulting increase in assembly steps, which poses a problem.

[0006] On the other hand, methods of fixing insulating sheets using adhesives or pressure-sensitive adhesives are also known, but there is a concern that fixing methods using adhesives or pressure-sensitive adhesives may lose their fixing strength due to the effects of heat, vibration, etc.

[0007] An object of the present invention is to provide an insulating sheet fixing structure that has a small number of parts and assembly steps and is less susceptible to a decrease in fixing strength due to heat, vibration, etc., and a manufacturing method that can easily produce such an insulating sheet fixing structure. [Means for solving the problem]

[0008] These objects can be achieved by the present invention as set forth in (1) to (13) below. (1) an insulating sheet made of a resin material; a protected object to which the insulating sheet is fixed and which is insulated and protected by the insulating sheet; Equipped with the object to be protected comprises a substrate having a first surface and a second surface which are opposite surfaces to each other, and a through-hole which penetrates the substrate from the first surface to the second surface; The insulating sheet fixing structure is characterized in that the insulating sheet has a flat portion that extends flat along the first surface, an extension portion that is located outside the through hole on the second surface, and a connecting portion that connects the flat portion and the extension portion and is inserted into the through hole.

[0009] (2) The insulating sheet fixing structure according to (1) above, wherein the extension portion and the connecting portion are thermoformed portions.

[0010] (3) The insulating sheet fixing structure according to (1) or (2), wherein the insulating sheet does not have a hole penetrating in the thickness direction.

[0011] (4) The insulating sheet fixing structure according to any one of (1) to (3) above, wherein the extension portion expands to surround the through hole when the second surface is viewed in plan.

[0012] (5) The insulating sheet fixing structure according to (4) above, wherein the width of the expansion portion in the radial direction of the through hole is 0.5 mm or more.

[0013] (6) The insulating sheet fixing structure according to any one of (1) to (5) above, wherein the insulating sheet has a thickness of 0.02 mm or more and 1.50 mm or less.

[0014] (7) The insulating sheet fixing structure according to any one of (1) to (6) above, wherein the object to be protected is a housing that houses a voltage application unit to which a voltage is applied.

[0015] (8) The insulating sheet fixing structure according to any one of (1) to (6) above, wherein the object to be protected is a mounting board.

[0016] (9) The insulating sheet fixing structure according to any one of (1) to (6), wherein the object to be protected is a bus bar structure.

[0017] (10) The insulating sheet fixing structure according to any one of (1) to (9), wherein the insulating sheet is made primarily of a thermoplastic resin.

[0018] (11) The insulating sheet fixing structure according to (10) above, wherein the thermoplastic resin is an aromatic polycarbonate resin or a polymer alloy containing an aromatic polycarbonate.

[0019] (12) The insulating sheet fixing structure according to any one of (1) to (11) above, wherein the insulating sheet contains a flame retardant made of a nitrogen-containing compound.

[0020] (13) A method for manufacturing the insulating sheet fixing structure according to any one of (1) to (12) above, a step of preparing a molded sheet having the flat plate portion and a convex molded portion molded so as to protrude from the flat plate portion, inserting the convex molded portion into the through hole from the first surface side, and causing a tip end of the convex molded portion to protrude to the second surface side; a step of performing a thermoforming process so as to expand the tip of the convex molded portion to form the expanded portion; 10. A method for manufacturing an insulating sheet fixing structure, comprising: [Effects of the Invention]

[0021] According to the insulating sheet fixing structure of the present invention, it is possible to obtain an insulating sheet fixing structure which has a small number of parts and assembly steps, and in which the fixing force is less likely to decrease due to heat, vibration, or the like.

[0022] Furthermore, the method for manufacturing an insulating sheet fixing structure according to the present invention allows for easy manufacturing of an insulating sheet fixing structure with a reduced number of parts and assembly steps, and with which the fixing strength is less likely to decrease due to heat, vibration, etc. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view showing an insulating sheet and a housing to which the insulating sheet fixing structure according to the first embodiment is applied. [Figure 2] 2 is a plan view of an insulating sheet fixed to the lid shown in FIG. 1, viewed from above. [Figure 3] FIG. 2 is a partially enlarged view of FIG. [Figure 4] FIG. 4 is a cross-sectional view showing an insulating sheet according to a modified example of the first embodiment. [Figure 5] 5A to 5C are process diagrams illustrating a method for manufacturing the insulating sheet fixing structure according to the first embodiment. [Figure 6] 6 is a partial cross-sectional view illustrating a method for manufacturing the fixing structure of the insulating sheet shown in FIG. 5. FIG. [Figure 7] 6 is a partial cross-sectional view illustrating a method for manufacturing the fixing structure of the insulating sheet shown in FIG. 5. FIG. [Figure 8] 10 is a cross-sectional view showing an insulating sheet and a mounting substrate to which the insulating sheet fixing structure according to the second embodiment is applied. FIG. [Figure 9] 10 is a plan view showing an insulating sheet and bus bar structure to which the insulating sheet fixing structure according to the third embodiment is applied. FIG. [Figure 10] 10 is a cross-sectional view of the insulating sheet fixing structure taken along line AA in FIG. 9. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An insulating sheet fixing structure and a method for manufacturing the insulating sheet fixing structure according to the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0025] 1. First embodiment First, as the fixing structure of the insulating sheet according to the first embodiment, a housing that houses the voltage application unit and an insulating sheet fixed to the housing will be described.

[0026] FIG. 1 is a cross-sectional view showing an insulating sheet 5 and a housing 20 (protected body) to which an insulating sheet fixing structure 1 according to the first embodiment is applied. FIG. 2 is a plan view, viewed from above, of the insulating sheet 5 fixed to the lid portion 22 shown in FIG. 1. In each drawing of the present application, three mutually orthogonal axes, an X-axis, a Y-axis, and a Z-axis, are set, and each axis is indicated by an arrow. The base end side of the arrow is referred to as the negative side of each axis, and the tip end side is referred to as the positive side of each axis. Furthermore, the positive side of the Z-axis is referred to as "up" and the negative side of the Z-axis is referred to as "down."

[0027] The insulating sheet fixing structure 1 shown in FIG. The housing 20 is a protected body that is insulated and protected by the insulating sheet 5. The housing 20 shown in FIG. 1 is a case that houses a mounting board 9 serving as a voltage application unit to which a voltage is applied, and includes a housing 21 and a lid 22. The housing 21 is box-shaped with an open top and a closed bottom. The lid 22 is plate-shaped and extends along the XY plane so as to cover the opening of the housing 21. The lid 22 also includes a base 222 having a first surface 231 and a second surface 232 that are opposite surfaces, and a through-hole 224 that penetrates the base 222 from the first surface 231 to the second surface 232.

[0028] The insulating sheet 5 is fixed to the housing 20 and insulates and protects the housing 20. Specifically, the insulating sheet 5 shown in FIG. 1 is fixed to the lid portion 22 and improves the insulation between the mounting board 9 and the lid portion 22, thereby insulating and protecting the lid portion 22. This makes it possible to suppress the occurrence of dielectric breakdown and corona discharge due to high electric field stress when a voltage is applied to the mounting board 9. Furthermore, providing the insulating sheet 5 makes it possible to suppress tracking due to creeping discharge on the first surface 231 of the lid portion 22. Furthermore, using a highly flame-retardant material for the insulating sheet 5 makes it possible to suppress burn damage to the insulating sheet 5.

[0029] The insulating sheet 5 is molded to fit the shape of the lid portion 22. Specifically, the insulating sheet 5 shown in FIG. 1 has a flat plate portion 52, an expanding portion 54, and a connecting portion 56. The flat plate portion 52 extends in a flat plate shape along the first surface 231. When viewed from above, the expanding portion 54 is located outside the through-hole 224 on the second surface 232. The connecting portion 56 connects the flat plate portion 52 and the expanding portion 54, and is inserted into the through-hole 224.

[0030] In this type of insulating sheet fixing structure 1, the base 222 is sandwiched between the flat plate portion 52 and the extension portion 54, and thus the insulating sheet 5 is fixed to the lid portion 22. Therefore, the fixing method shown in Fig. 1 is less susceptible to the effects of heat and vibration and less likely to experience a decrease in fixing force than fixing methods that use adhesives or pressure-sensitive adhesives. Furthermore, in the insulating sheet fixing structure 1 shown in Fig. 1, the fixing force is generated by the shape of the insulating sheet 5 itself, so the number of parts can be kept small, and therefore the assembly man-hours can also be kept small.

[0031] 1.1.Housing As described above, the case 20 has the housing 21 and the lid 22. Inside the case 20, the mounting board 9 is accommodated.

[0032] The housing 21 has a bottom that extends along the XY plane and walls that rise upward from the outer edge of the bottom. A mounting board 9 is accommodated inside the housing 21. The mounting board 9 includes a wiring board 90 having wiring (not shown), and a power semiconductor element 91 and a bus bar 92 mounted on the wiring board 90. The mounting board 9 is fixed to the housing 21, for example, by fixing screws (not shown). The lid 22 is provided to close the opening of the housing 21. This allows the mounting board 9 to be stably protected from the external environment.

[0033] As described above, the lid portion 22 has the base 222 and the through hole 224. As described above, the connecting portion 56 of the insulating sheet 5 is disposed within the through hole 224, and the extending portion 54 is disposed on the second surface 232 side of the base 222. Therefore, the extending portion 54 and the connecting portion 56 function as a fixing means for fixing the insulating sheet 5 to the lid portion 22.

[0034] 2 has a circular shape when viewed from above (when the second surface 232 is viewed in plan view). This prevents the extension portion 54 from slipping out of the through hole 224, for example, even when the insulating sheet 5 rotates around the Z axis relative to the cover portion 22.

[0035] The shape of the through-hole 224 is not limited to this, and may be elliptical, oval, polygonal, or any other shape.

[0036] The thickness of the base 222 (the length of the through hole 224) is not particularly limited, but is preferably 0.1 mm to 100 mm, more preferably 0.3 mm to 50 mm, and even more preferably 0.5 mm to 20 mm. If the thickness of the base 222 is below the lower limit, the mechanical strength of the base 222 may be insufficient, and the insulating sheet 5 may not be sufficiently fixed. On the other hand, if the thickness of the base 222 is above the upper limit, it may be more difficult to form the connecting portion 56 by thermoforming, for example.

[0037] Examples of materials for the housing 21 and the lid 22 include metal materials, ceramic materials, and resin materials. A composite material using two or more of these materials may also be used. Among these, metal materials are useful as materials for the housing 21 and the lid 22 because of their excellent thermal conductivity and mechanical properties. Furthermore, metal materials often have excellent electrical conductivity and magnetic permeability, which allows the housing 21 and the lid 22 to be used as electromagnetic shields or magnetic field shields.

[0038] On the other hand, when a metal material is used, there is a concern that the insulation may be reduced or discharge may occur between the mounting substrate 9 and the housing 20. In particular, between the top surface of the mounting substrate 9 and the first surface 231 of the lid portion 22, the distance between the portion to which voltage is applied and the lid portion 22 is short, so there is a risk of a reduction in the withstand voltage or discharge.

[0039] In contrast, in the insulating sheet fixing structure 1 shown in FIG. 1 , the insulating sheet 5 is fixed so as to cover the first surface 231 of the lid portion 22. This reduces the probability of a decrease in the withstand voltage and discharge, and provides the same effect as increasing the spatial distance between the mounting board 9, which is the voltage application section, and the lid portion 22. Therefore, by using the insulating sheet 5, it is possible to achieve a high withstand voltage without increasing the size of the housing 20. As a result, it is possible to improve the electrical reliability of the insulating sheet fixing structure 1, and to make the housing 20 smaller and thinner without impairing electrical reliability.

[0040] 1.2. Mounting board As described above, the mounting substrate 9 includes the wiring board 90, and the power semiconductor element 91 and bus bar 92 as voltage application units. The power semiconductor element 91 and bus bar 92 shown in FIG. 1 protrude upward from the upper surface of the wiring board 90, for example.

[0041] The power semiconductor element 91 is a semiconductor element that performs high-power switching, etc. Examples of the power semiconductor element 91 include an IGBT (insulated gate bipolar transistor) and a power MOSFET (metal oxide semiconductor field effect transistor).

[0042] The bus bar 92 is a conductor that connects the wiring board 90 to a power supply line (not shown). The bus bar 92 is made of, for example, a metal plate or rod. The bus bar 92 shown in FIG. 1 protrudes upward from the upper surface of the wiring board 90 and is bent sideways (towards the negative X-axis) midway. However, the shape of the bus bar 92 is not limited to this.

[0043] At least one of the power semiconductor element 91 and the bus bar 92 is used in a state where a high voltage is applied. The applied voltage is, for example, 50 V or more, and in many cases, 71 V or more and 10 kV or less. Even when such a high voltage is applied to the mounting board 9, the use of the insulating sheet 5 allows the housing 20 to be made smaller and thinner.

[0044] The voltage application unit housed in the housing 20 is not limited to the mounting board 9, and may be any object to which a voltage is applied. Examples of the voltage application unit include a battery, a capacitor, a diode, a coil, a resistor, a relay, a transformer, a switch, a connector, a terminal, etc., and may be an object containing one or more of these.

[0045] In addition, components that are not directly subjected to voltage but are in contact with components to which voltage is directly applied may also be subject to unintentional voltage application, and are therefore also included in the "voltage application section." Specific examples of such components include heat sinks, heat spreaders, and heat pipes.

[0046] 1.3.Insulation sheet 1.3.1. Overview of Insulation Sheets As described above, the insulating sheet 5 is fixed to the lid portion 22 and insulates and protects the lid portion 22. The insulating sheet 5 shown in FIG. 1 has a flat portion 52, an extension portion 54, and a connecting portion 56. The flat portion 52 is provided on the first surface 231 side, and the extension portion 54 is provided on the second surface 232 side, via the connecting portion 56 provided in the through hole 224 of the lid portion 22. In this way, the insulating sheet 5 is fixed to the lid portion 22. As described above, this fixing method can reduce the number of parts and therefore the assembly man-hours.

[0047] 1 and 2, the flat plate portion 52 extends in a flat plate shape along the first surface 231. This makes it possible to sufficiently reduce the number of electrical paths between the mounting board 9 and the lid portion 22, thereby sufficiently improving insulation. In addition, it is possible to minimize the effect of the flat plate portion 52 on the volume inside the housing 20, thereby ensuring sufficient space to accommodate the mounting board 9.

[0048] As shown in FIG. 2, the flat plate portion 52 may be provided so as to cover substantially the entire first surface 231, or may be provided so as to cover only a portion of the first surface 231.

[0049] FIG. 3 is a partial enlarged view of FIG. 1. The extension portion 54 shown in FIG. 3 extends outward from the through-hole 224. This prevents the extension portion 54 from being pulled into the through-hole 224 even when a tensile load is applied. In other words, the extension portion 54 functions as a stopper that prevents the insulating sheet 5 from being released from its fixed position. This effect is also well maintained even in an environment where heat, vibration, etc. are applied. This makes it possible to realize an insulating sheet fixing structure 1 that is less likely to lose its fixing strength even in such an environment.

[0050] 2 expands to surround the through-hole 224. This configuration particularly enhances the fixing force of the insulating sheet 5 provided by the expansion portion 54 compared to when the expansion portion 54 expands in only one direction, such as the positive side of the X-axis in FIG. 2, with the through-hole 224 as the reference point. Furthermore, even when a load is applied to the insulating sheet 5, a decrease in the fixing force can be suppressed regardless of the direction of the load.

[0051] The external shape of the extension 54 when viewed from above may be a circle as shown in FIG. 2, or may be any other shape, such as a polygon, an ellipse, an oval, or any other irregular shape.

[0052] The direction extending radially from the center of through-hole 224 is defined as the "radial direction of through-hole 224." When viewed from above, the radial width of the portion located outside through-hole 224, i.e., the width W of extension portion 54 shown in FIG. 3, is preferably 0.5 mm or more, more preferably 1.0 mm or more and 20 mm or less, and even more preferably 1.5 mm or more and 10 mm or less. If width W of extension portion 54 is within the above range, extension portion 54 can more reliably perform its function as a stopper.

[0053] If the width W of the expansion portion 54 is less than the lower limit, there is a risk that the expansion portion 54 will be pulled into the through hole 224 when a tensile load is applied. On the other hand, the width W of the expansion portion 54 may exceed the upper limit, but in that case, the thickness of the expansion portion 54 will also increase, which may have adverse effects such as becoming a hindrance.

[0054] When the shape of the through-hole 224 is a shape other than a circle, the "radial direction of the through-hole 224" is defined as a direction that spreads radially from the center of the inscribed circle of the through-hole 224 when viewed from above.

[0055] The extension portion 54 and the connecting portion 56 are preferably thermoformed portions (thermoformed portions). Specifically, the extension portion 54 and the connecting portion 56 are preferably formed by thermoforming a sheet-like base material using a mold of a predetermined shape. In this case, the constituent materials are continuous at the boundary between the flat portion 52 and the connecting portion 56, and at the boundary between the connecting portion 56 and the extension portion 54, ensuring integrity. This makes it easier to prevent breakage and the like even when a load is applied.

[0056] The width W is determined by measuring the width of the expansion portion 54 at 10 or more locations and averaging the measurements.

[0057] The number of extension portions 54 and connecting portions 56 that the insulating sheet 5 has may be one or more, but from the viewpoint of stably fixing the insulating sheet 5, it is preferable that the number of each is two or more, and more preferably four or more. On the other hand, an upper limit does not need to be set, but considering the balance between fixing strength and the man-hours required for fixing, it is preferable that the number of each is 20 or less, and more preferably 10 or less.

[0058] Furthermore, the insulating sheet 5 may have holes penetrating in the thickness direction, but preferably does not have any holes. This increases the mechanical strength of the insulating sheet 5. In particular, by not providing holes penetrating the extensions 54, the mechanical strength of the extensions 54 can be increased. As a result, an insulating sheet 5 with particularly high fixing strength is obtained.

[0059] Note that insulating sheet 5 may be formed into a shape other than the above. For example, if first surface 231 of lid portion 22 has an uneven shape, part of flat portion 52 of insulating sheet 5 may be formed into an uneven shape to follow the uneven shape. Furthermore, part of flat portion 52 of insulating sheet 5 may be formed into an uneven shape to follow the upper surface of mounting substrate 9.

[0060] The thickness of the insulating sheet 5 is not particularly limited, but is preferably 0.02 mm to 1.50 mm, more preferably 0.03 mm to 1.20 mm, and even more preferably 0.05 mm to 0.90 mm. This results in an insulating sheet 5 with excellent flame retardancy, tracking resistance, and insulation properties. Furthermore, the extension portions 54 and connecting portions 56 can be easily and quickly formed by thermoforming.

[0061] If the thickness of the insulating sheet 5 is below the lower limit, the flame retardancy, tracking resistance, and insulating properties may be reduced. On the other hand, the thickness of the insulating sheet 5 may exceed the upper limit, but in that case, the accuracy of forming the connecting portion 56 may be reduced. The thickness of the insulating sheet 5 refers to the thickness of the flat portion 52.

[0062] The thickness of the extension portion 54 is not particularly limited, but is preferably 20% or more of the thickness of the insulating sheet 5, more preferably 40% to 300% of the thickness of the insulating sheet 5, and even more preferably 50% to 200%. This makes it possible to reduce adverse effects associated with an excessive thickness of the extension portion 54 while ensuring sufficient mechanical strength of the extension portion 54. The thickness of the extension portion 54 is measured on the inner surface of the through hole 224.

[0063] Furthermore, the insulating sheet 5 may have other portions than those described above. Examples of such portions include portions with irregularities or creases that conform to the first surface 231 of the lid portion 22, portions with irregularities or creases for the purpose of increasing rigidity, portions that are fixed to the lid portion 22 in a shape other than those described above, and other portions with any other shape. These portions are also preferably thermoformed portions.

[0064] 1.3.2. Materials of the insulating sheet The insulating sheet 5 is made of a resin material. The proportion of the resin material in the constituent materials of the insulating sheet 5 is preferably 60 mass % or more, more preferably 70 mass % or more, and even more preferably 80 mass % or more. This results in an insulating sheet 5 that is excellent in insulation properties and formability, and is easy to reduce in weight.

[0065] Examples of resin materials include various thermoplastic resins such as polyolefin resin, polyamide resin, polyester resin, aliphatic polycarbonate resin, aromatic polycarbonate resin, heat-resistant polycarbonate resin, polyarylate resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polylactic acid, styrene copolymer, polyacetal resin, polyphenylene ether resin, polyphenylene sulfide resin, polymethyl methacrylate resin, and cellulose ester resin, as well as various thermosetting resins such as polyimide, polyurethane, epoxy resin, and phenolic resin. The resin material may be a combination of one or more of these resins.

[0066] Furthermore, the insulating sheet 5 is preferably made primarily of a thermoplastic resin. The "primary material" refers to the above-mentioned ratio. A sheet made primarily of a thermoplastic resin can be plastically deformed by heat, and is therefore excellent in secondary processability. This allows for the insulating sheet 5 to be easily manufactured using thermoforming.

[0067] Among these, polyolefin resin, polyamide resin, aliphatic polycarbonate resin, aromatic polycarbonate resin, or heat-resistant polycarbonate resin is preferably used as the thermoplastic resin. Of these, polymer alloys containing aromatic polycarbonate resin are preferably used as the thermoplastic resin. This allows for the insulating sheet 5 to have excellent heat resistance and flame retardancy due to the aromatic ring structure.

[0068] Furthermore, a resin material with high tracking resistance is preferably used. Tracking resistance refers to the resistance to the phenomenon in which a conductive path (tracking) is formed due to discharge occurring on the surface of an insulator. Such tracking resistance can be quantified, for example, by the comparative tracking index (CTI), which is an index of tracking resistance measured in accordance with ASTM D3638.

[0069] The comparative tracking index CTI of the resin material is preferably at least 400 V, and more preferably at least 600 V. This makes it possible to obtain an insulating sheet 5 with particularly good tracking resistance.

[0070] The glass transition temperature Tg of the resin material is preferably 125°C or higher, and more preferably 130°C or higher but lower than 200°C. This provides heat resistance to the resin material, making it easier to suppress coloration due to carbonization even if creeping discharge occurs in the insulating sheet 5. As a result, the occurrence of poor appearance in the insulating sheet 5 and the deterioration of insulating properties due to carbonization can be suppressed. The glass transition temperature Tg of the resin material is measured by DSC (differential scanning calorimetry). The heating rate in the DSC method is 10°C / min.

[0071] 1.3.2.1. Polyolefin resin Examples of polyolefin resins include high-density polyethylene resins, polypropylene resins, polybutene resins, ethylene-(meth)acrylic acid copolymers, ethylene-methyl (meth)acrylate copolymers, ethylene-ethyl (meth)acrylate copolymers, ethylene-vinyl acetate copolymers, maleic anhydride-modified polyethylene, carboxylic acid-modified polyethylene, ethylene-propylene copolymers, and ethylene-propylene-diene copolymers.

[0072] Polyolefin resins have excellent chemical resistance against various chemicals. In addition, polyolefin resins have good tracking resistance due to their hydrocarbon chain structure. Therefore, polyolefin resins contribute to improving the chemical resistance and tracking resistance of insulating sheet 5.

[0073] Of these, polypropylene resin is preferably used, which particularly improves the chemical resistance and tracking resistance of the insulating sheet 5.

[0074] Polyamide resin Examples of polyamide resins include polycaproamide (polyamide 6), polytetramethylene adipamide (polyamide 46), polyhexamethylene adipamide (polyamide 66), polyhexamethylene sebacamide (polyamide 610), polyhexamethylene dodecamide (polyamide 612), polyundecamethylene adipamide (polyamide 116), polyundecane amide (polyamide 11), polydodecanamide (polyamide 12), polytrimethylhexamethylene terephthalamide (polyamide TMHT), polyhexamethylene terephthalamide (polyamide 6T), polyhexamethylene isophthalamide (polyamide 6I), and polyhexamethylene sebacamide (polyamide 610). Examples of suitable polyamides include ethylene terephthalic / isophthalamide (polyamide 6T / 6I), polybis(4-aminocyclohexyl)methanedodecamide (polyamide PACM12), polybis(3-methyl-4-aminocyclohexyl)methanedodecamide (polyamide dimethyl PACM12), polymetaxylylene adipamide (polyamide MXD6), polynonamethylene terephthalamide (polyamide 9T), polydecamethylene terephthalamide (polyamide 10T), polyundecamethylene terephthalamide (polyamide 11T), and polyundecamethylene hexahydroterephthalamide (polyamide 11T(H)), and copolymers or mixtures thereof may also be used.

[0075] The polyamide resin can be obtained by polymerizing or copolymerizing nylon salt made of diamine and dicarboxylic acid as a raw material using a known method such as melt polymerization, solution polymerization, solid-state polymerization, etc. By using a polyamide resin as the resin material, the tracking resistance of the insulating sheet 5 can be further improved.

[0076] The diamine may be an aliphatic diamine, but an alicyclic diamine or aromatic diamine is preferably used, and an alicyclic diamine is more preferably used. By using these, a polyamide resin having a cyclic structure such as an aromatic ring structure or an alicyclic structure can be prepared. Such a polyamide resin contributes to improving the heat resistance of the insulating sheet 5. Furthermore, the alicyclic diamine in particular contributes to improving the tracking resistance of the insulating sheet 5.

[0077] Examples of alicyclic diamines include 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 1,3-cyclohexanedimethylamine, 1,4-cyclohexanedimethylamine, bis(4-aminocyclohexyl)methane, bis(4-aminocyclohexyl)propane, bis(3-methyl-4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)propane, 5-amino-2,2,4-trimethyl-1-cyclopentanemethylamine, 5-amino-1,3,3-trimethylcyclohexanemethylamine (isophoronediamine), bis(aminopropyl)piperazine, bis(aminoethyl)piperazine, norbornanedimethylamine, and tricyclodecanedimethylamine, and one or more of these may be used.

[0078] Examples of aromatic diamines include m-xylylenediamine and p-xylylenediamine.

[0079] The dicarboxylic acid may be an alicyclic dicarboxylic acid or an aromatic dicarboxylic acid, but an aliphatic dicarboxylic acid is preferably used. This allows the preparation of a polyamide resin having a hydrocarbon chain structure. Such a polyamide resin contributes to improving the tracking resistance of the insulating sheet 5.

[0080] Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, octadecanedioic acid, and eicosanedioic acid; alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, dicyclohexanemethane-4,4'-dicarboxylic acid, and norbornanedicarboxylic acid; and aromatic dicarboxylic acids such as isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. One or more of these may be used.

[0081] As the polyamide resin, polyamide 6T, polyamide PACM12, polyamide dimethyl PACM12, polyamide MXD6, polyamide 9T, polyamide 10T, polyamide 11T, or polyamide 11T(H) is preferably used, and polyamide PACM12 or polyamide dimethyl PACM12 is more preferably used. These have both a cyclic structure such as an aromatic ring structure or an alicyclic structure, and a structure derived from an aliphatic monomer, and therefore contribute to improving both the heat resistance and tracking resistance of the insulating sheet 5. Polyamide PACM12 contains a structural unit represented by the following formula (2).

[0082] [ka]

[0083] The polyamide PACM12 is synthesized from bis(4-aminocyclohexyl)methane (PACM) and dodecanedioic acid. Polyamide dimethyl PACM12 contains a structural unit represented by the following formula (3).

[0084] [ka]

[0085] The polyamide dimethyl PACM12 is synthesized using bis(3-methyl-4-aminocyclohexyl)methane (MACM) and dodecanedioic acid as raw materials.

[0086] Aliphatic polycarbonate resin Examples of aliphatic polycarbonate resins include those containing an aliphatic carbonate unit having a carbon number of 2 to 12. Specific examples include polyethylene carbonate, polypropylene carbonate, polytrimethylene carbonate, polytetramethylene carbonate, polypentamethylene carbonate, polyhexamethylene carbonate, polyheptamethylene carbonate, polyoctamethylene carbonate, polynonamemethylene carbonate, polydecamethylene carbonate, polyoxydiethylene carbonate, poly-3,6-dioxyoctane carbonate, poly-3,6,9-trioxyundecane carbonate, polyoxydipropylene carbonate, polycyclopentene carbonate, and polycyclohexene carbonate.

[0087] The aliphatic polycarbonate resin may also be a resin containing an aliphatic carbonate unit containing a diol residue represented by the following formula (4).

[0088] [ka] (In formula (4), R 5 ~R 8 are each independently a hydrogen atom, an alkyl group, a cycloalkyl group, or an aryl group.

[0089] The aliphatic polycarbonate resin preferably contains 30 mol % to 100 mol %, and more preferably 50 mol % to 90 mol %, of all structural units of the aliphatic carbonate unit containing the diol residue represented by the above formula (4).

[0090] The diol residue represented by the above formula (4) has a structure in which two tetrahydrofuran rings are fused together. By including such a structure in the structural unit, the glass transition temperature Tg of the aliphatic polycarbonate resin can be increased. As a result, an insulating sheet 5 having excellent heat resistance and tracking resistance can be obtained.

[0091] Examples of diols constituting the diol residue represented by the above formula (4) include isosorbide, isomannide, isoidide, etc. These carbohydrate-derived diols are useful in that they are substances that can also be obtained from natural biomass.

[0092] 1.3.2.4. Aromatic polycarbonate resin Aromatic polycarbonate resins can be obtained by the phosgene method in which various dihydroxydiaryl compounds are reacted with phosgene, the transesterification method in which a dihydroxydiaryl compound is reacted with a carbonate ester such as diphenyl carbonate, the ring-opening polymerization method of a cyclic carbonate compound, the interfacial polycondensation method, etc. Such aromatic polycarbonate resins impart excellent heat resistance and flame retardancy derived from the aromatic ring structure to the insulating sheet 5.

[0093] Dihydroxydiaryl compounds include, in addition to bisphenol A, bis(hydroxyaryl)alkanes such as bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)octane, bis(4-hydroxyphenyl)phenylmethane, 2,2-bis(4-hydroxyphenyl-3-methylphenyl)propane, and 1,1-bis(4-hydroxy-3-tert-butylphenyl)propane; and bis(hydroxyaryl)cycloalkanes such as 1,1-bis(4-hydroxyphenyl)cyclopentane and 1,1-bis(4-hydroxyphenyl)cyclohexane. dihydroxydiaryl ethers such as 4,4'-dihydroxydiphenyl ether and 4,4'-dihydroxy-3,3'-dimethyldiphenyl ether, dihydroxydiaryl sulfides such as 4,4'-dihydroxydiphenyl sulfide and 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfide, dihydroxydiaryl sulfoxides such as 4,4'-dihydroxydiphenyl sulfoxide and 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfone, dihydroxydiaryl sulfones such as 4,4'-dihydroxydiphenyl sulfone and 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfone, etc. These may be used alone or in combination of two or more.

[0094] The aromatic polycarbonate resin particularly includes those having a structural unit represented by the following formula (1).

[0095] [ka] (In formula (1), R 1 and R 2 are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom. m and n are independently an integer of 0 to 4. X is a direct bond, O, S, SO, SO2, CR 3 R 4(R 3 and R 4 are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and may be the same or different from each other.), an alkylene group having 2 to 10 carbon atoms, a polydimethylsiloxane group, or C(CF3)2.

[0096] The aromatic polycarbonate resin having the structural unit represented by the above formula (1) imparts particularly excellent heat resistance and flame retardancy to the insulating sheet 5.

[0097] Of all the structural units constituting the aromatic polycarbonate resin, the proportion of the structural units represented by the above formula (1) is preferably 55 mol % or more, more preferably 70 mol % or more, and even more preferably 80 mol % or more.

[0098] In addition, from the viewpoint of ease of acquisition and cost, R 1 and R 2 are each preferably a hydrogen atom, and X is preferably CR 3 R 4 and R 3 and R 4 are preferably each a methyl group or a hydrogen atom.

[0099] The aromatic polycarbonate resin is preferably a polycarbonate resin having structural units derived from bisphenol A (2,2-bis(4-hydroxyphenyl)propane), which can further improve the flame retardancy and heat resistance of the insulating sheet 5.

[0100] The viscosity average molecular weight (M) of the aromatic polycarbonate resin is not particularly limited, but is preferably 5,000 or more and 100,000 or less, more preferably 12,000 or more and 35,000 or less, even more preferably 15,000 or more and 30,000 or less, and particularly preferably 18,000 or more and 28,000 or less.

[0101] The viscosity average molecular weight (M) is calculated from the viscosity (η) of the methylene chloride solution of the resin, η = kM α The viscosity is calculated using the formula below. k and α are constants specific to polymers. Viscosity is measured using an Ubbelohde viscometer at 20°C.

[0102] The aromatic polycarbonate resin may also be a blend of a resin with a high viscosity average molecular weight (high viscosity resin) and a resin with a low viscosity average molecular weight (low viscosity resin), thereby providing an insulating sheet 5 with excellent moldability without impairing the heat resistance and flame retardancy inherent to the aromatic polycarbonate resin.

[0103] The difference between the viscosity average molecular weight of the high-viscosity resin and the viscosity average molecular weight of the low-viscosity resin is not particularly limited, but is preferably from 3,000 to 20,000, and more preferably from 5,000 to 10,000. This allows for an insulating sheet 5 with particularly good formability to be obtained.

[0104] When the blending amount of the high-viscosity resin is M1 and the blending amount of the low-viscosity resin is M2, the blending ratio M1 / M2 is preferably 0.5 to 8.0 in mass ratio, more preferably 0.8 to 6.0 in mass ratio, and even more preferably 0.9 to 5.0 in mass ratio, which results in an insulating sheet 5 with particularly good formability.

[0105] The glass transition temperature Tg of the aromatic polycarbonate resin is preferably 130°C or higher and lower than 160°C, and more preferably 140°C or higher and 155°C or lower. If the glass transition temperature Tg of the aromatic polycarbonate resin is within the above range, the heat resistance and flame retardancy of the insulating sheet 5 can be sufficiently improved. The glass transition temperature Tg of the aromatic polycarbonate resin is measured by a differential scanning calorimeter (DSC) method. The heating rate in the DSC method is 10°C / min.

[0106] The content of aromatic polycarbonate resin in insulating sheet 5 is not particularly limited, but is preferably 70% by mass or more, and more preferably 80% by mass or more.

[0107] 1.3.2.5.Heat-resistant polycarbonate resin An example of a heat-resistant polycarbonate resin is a resin containing a carbonate unit (bisphenol isophorone carbonate unit) represented by the following formula (5). Such a polycarbonate resin has higher heat resistance than an aromatic polycarbonate resin. Hereinafter, a polycarbonate resin containing a bisphenol isophorone carbonate unit will be referred to as a "heat-resistant polycarbonate resin."

[0108] [ka] (In formula (5), R a and R b are each independently an alkyl group having 1 to 12 carbon atoms, and R g is an alkyl group having 1 to 12 carbon atoms, p and q each independently represent an integer of 0 to 4, and t represents an integer of 0 to 10.

[0109] In addition, each R a and R b Preferably, at least one of is positioned meta to the cyclohexylidene bridging group.

[0110] Also, R a and R b are each independently an alkyl group having 1 to 4 carbon atoms, and R g is an alkyl group having 1 to 4 carbon atoms, p and q are each 0 or 1, and t may be 0 to 5. Furthermore, R a , R b , and R g are each a methyl group, p and q are each 0 or 1, and t is 0 or 3, preferably 0.

[0111] A specific example of such a heat-resistant polycarbonate resin is a resin containing carbonate units (bisphenol A carbonate units) derived from bisphenol A (2,2-bis(4-hydroxyphenyl)propane) and carbonate units (bisphenol isophorone carbonate units) represented by formula (5). In this case, p and q in the bisphenol isophorone carbonate units are each 0, and each R g is preferably a methyl group, and t is preferably 3. This makes the bisphenol isophorone carbonate unit a carbonate unit containing a structure derived from bisphenol TMC (1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane).

[0112] Such bisphenol isophorone carbonate units contain both an aromatic ring structure and an alicyclic structure, and therefore contribute particularly to improving both the heat resistance (flame retardancy) and tracking resistance of insulating sheet 5.

[0113] Of all structural units constituting the heat-resistant polycarbonate resin, the proportion of bisphenol isophorone carbonate units is preferably 30 mol % or more, more preferably 50 mol % or more, and even more preferably 55 mol % or more, which contributes to improving both the heat resistance (flame retardancy) and tracking resistance of the insulating sheet 5.

[0114] The glass transition temperature Tg of the heat-resistant polycarbonate resin is preferably 160° C. or higher and 230° C. or lower, and more preferably 165° C. or higher and 220° C. or lower. When the glass transition temperature Tg of the heat-resistant polycarbonate resin is within the above range, the heat resistance of the insulating sheet 5 can be particularly improved. This makes it possible to particularly suppress coloration due to carbonization even when creeping discharge occurs in the insulating sheet 5, thereby particularly suppressing the occurrence of poor appearance and the deterioration of insulating properties due to carbonization.

[0115] If the glass transition temperature Tg is below the lower limit, there is a risk that poor appearance or carbonization due to creeping discharge may occur easily, whereas if the glass transition temperature Tg is above the upper limit, there is a risk that the molding temperature of the heat-resistant polycarbonate resin may become too high, which may result in molding defects.

[0116] 1.3.2.6. Polymer alloys The constituent material of the insulating sheet 5 may include a polymer alloy (a polymer alloy containing aromatic polycarbonate) formed by alloying an aromatic polycarbonate resin with a compatible resin. A polymer alloy refers to a single-phase material or a stable multi-phase material formed by mixing multiple types of polymers, preferably a single-phase material. In this specification, "alloying" refers to the preparation of such a single-phase or multi-phase material by kneading raw materials containing multiple types of polymers. In particular, alloying an aromatic polycarbonate resin with a compatible resin provides an insulating sheet 5 that combines the heat resistance inherent in the aromatic polycarbonate resin with other properties inherent in the compatible resin.

[0117] The compatible resin preferably used is the polyolefin resin, polyamide resin, aliphatic polycarbonate resin, heat-resistant polycarbonate resin, or the like, as described above. In this case, the aromatic polycarbonate resin alloyed with this compatible resin is preferably a resin having a structural unit represented by the above formula (1). In such a combination, the compatible resin has a higher tracking resistance (comparative tracking index CTI) than the aromatic polycarbonate resin having the structural unit represented by the above formula (1). This allows for an insulating sheet 5 that has both heat resistance and tracking resistance.

[0118] The proportion of the compatible resin in the polymer alloy is not particularly limited, but is preferably 5% by mass to 80% by mass, more preferably 10% by mass to 75% by mass, even more preferably 20% by mass to 70% by mass, and particularly preferably 40% by mass to 65% by mass. This configuration makes it possible to realize a polymer alloy that has a good balance between the properties of the aromatic polycarbonate resin having the structural unit represented by formula (1), such as heat resistance and flame retardancy, and the properties of the compatible resin.

[0119] The comparative tracking index CTI of the compatible resin is preferably at least 400 V, and more preferably at least 600 V. This makes it possible to obtain an insulating sheet 5 with particularly good tracking resistance.

[0120] Furthermore, the comparative tracking index CTI of the compatible resin is preferably at least 50 V higher than the comparative tracking index CTI of the aromatic polycarbonate resin, and more preferably at least 100 V higher, thereby providing an insulating sheet 5 that better balances flame retardancy and tracking resistance.

[0121] The glass transition temperature Tg of the compatible resin is preferably 125° C. or higher, and more preferably 130° C. or higher and 230° C. or lower. This provides heat resistance to the compatible resin, which makes it easier to suppress coloration due to carbonization even if creeping discharge occurs in the insulating sheet 5. As a result, the occurrence of poor appearance in the insulating sheet 5 and the deterioration of insulating properties due to carbonization can be suppressed.

[0122] Here, the tracking resistance and glass transition temperature Tg of resins (compounds) that can be used for the insulating sheet 5 are exemplified. Table 1 below lists the CTI value, which indicates tracking resistance, and the glass transition temperature Tg for various resins. For aromatic polycarbonate resins, the viscosity average molecular weight is also listed.

[0123] [Table 1]

[0124] As shown in Table 1, aromatic polycarbonate resins tend to have slightly lower tracking resistance than other resins. For this reason, using aromatic polycarbonate resins in combination with other resins to form alloys is useful from the perspective of achieving the combined properties of both resins.

[0125] Furthermore, the compatible resin preferably has an aromatic ring ratio of 90% by mass or less, more preferably 70% by mass or less, even more preferably 50% by mass or less, and particularly preferably 30% by mass or less. Such a compatible resin has a relatively high ratio of aliphatic structures. This can impart good tracking resistance to the insulating sheet 5. This allows for the production of an insulating sheet 5 that is excellent in both flame retardancy and tracking resistance.

[0126] Furthermore, the proportion of aromatic rings in the entire polymer alloy is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. Such a polymer alloy has a relatively high proportion of aliphatic structures. This allows the insulating sheet 5 to have good tracking resistance. This allows the insulating sheet 5 to have both excellent flame retardancy and tracking resistance. Furthermore, even if creeping discharge occurs in the insulating sheet 5, coloring due to carbonization can be easily suppressed. As a result, the occurrence of poor appearance in the insulating sheet 5 and the deterioration of insulating properties due to carbonization can be suppressed.

[0127] The ratio of aromatic rings can be determined as follows: Here, as an example, the ratio of aromatic rings in carbonate units represented by the following formula is calculated.

[0128] [ka]

[0129] The carbonate unit has 16 carbon atoms, 3 oxygen atoms, and 14 hydrogen atoms. Therefore, the molecular weight of the carbonate unit is 254.

[0130] In addition, one aromatic ring has 6 carbon atoms and 4 hydrogen atoms. Therefore, the molecular weight of one aromatic ring is 12 × 6 + 1 × 4 = 76.

[0131] The number of aromatic rings in the carbonate unit is 2. Therefore, the ratio [mass %] of aromatic rings in the carbonate unit is 76×2 / 254×100=59.8.

[0132] Examples of compatible resins include polyolefin resins, polyamide resins, polyester resins, aliphatic polycarbonate resins, heat-resistant polycarbonate resins, polyarylate resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polylactic acid, styrene copolymers, polyacetal resins, polyphenylene ether resins, polyphenylene sulfide resins, polymethyl methacrylate resins, and cellulose ester resins. The compatible resin may be a combination of one or more of these resins. Among these, polyolefin resins, polyamide resins, aliphatic polycarbonate resins, and heat-resistant polycarbonate resins are preferably used.

[0133] The polymer alloy may contain resins other than the above components, that is, the polymer alloy may be an alloy of three or more resins.

[0134] An example of a method for preparing a polymer alloy will be described. First, the raw materials are premixed and melted and kneaded using a batch kneader, twin-screw extruder, or the like. This mechanically stirs the raw materials, resulting in a kneaded product containing a polymer alloy. The kneading and melting conditions are appropriately set depending on the type and blending ratio of the raw materials, and examples include a temperature of 200 to 250°C, a screw rotation speed of 300 to 1000 rpm, and a kneading time of approximately 3 to 20 minutes. Next, the kneaded product is pelletized as necessary.

[0135] Furthermore, a compatibilizer may be added to the raw materials as needed, which can further increase the compatibility of the resins to be alloyed.

[0136] The amount of the compatibilizer added is preferably 2 parts by mass or more and 30 parts by mass or less, and more preferably 5 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the resin.

[0137] Additives The insulating sheet 5 may contain any additives. Examples of additives include flame retardants, colorants, stabilizers, lubricants, processing aids, antistatic agents, antioxidants, neutralizing agents, UV absorbers, dispersants, thickeners, mold release agents, fillers, flow improvers, plasticizers, and antibacterial agents. The insulating sheet 5 may contain one type of additive, or two or more types in any combination.

[0138] Of these, the flame retardant enhances the flame retardancy of the insulating sheet 5 . Examples of the flame retardant include inorganic phosphorus-based flame retardants such as halogen-based flame retardants, red phosphorus and polyphosphate-based flame retardants such as ammonium polyphosphate, organic phosphorus-based flame retardants such as triaryl phosphate ester compounds, metal hydroxide-based compounds, antimony oxide-based compounds, nitrogen-containing compounds, etc. Furthermore, the flame retardant may be a combination of two or more of these.

[0139] Among these, phosphorus-based flame retardants or nitrogen-containing compounds are preferably used as the flame retardant, and nitrogen-containing compounds are more preferably used. When the flame retardant contains a nitrogen-containing compound, the flame retardancy of the insulating sheet 5 can be further improved. Furthermore, since the nitrogen-containing compound does not contain halogen atoms, a so-called halogen-free and fluorine-free insulating sheet 5 can be realized.

[0140] Examples of the nitrogen-containing compound include compounds having a triazine skeleton. Examples of compounds having a triazine skeleton include melamine, melamine derivatives such as butylmelamine, trimethylolmelamine, hexamethylolmelamine, hexamethoxymethylmelamine, and melamine phosphate, cyanuric acid, cyanuric acid derivatives such as methyl cyanurate, diethyl cyanurate, trimethyl cyanurate, and triethyl cyanurate, isocyanuric acid, isocyanuric acid derivatives such as methyl isocyanurate, N,N'-diethyl isocyanurate, trismethyl isocyanurate, trisethyl isocyanurate, bis(2-carboxyethyl) isocyanurate, 1,3,5-tris(2-carboxyethyl) isocyanurate, and tris(2,3-epoxypropyl) isocyanurate, melamine cyanurate, and melamine isocyanurate. These compounds can be used alone or in combination of two or more.

[0141] Among these, the compound having a triazine skeleton is preferably one or more melamine-based compounds selected from the group consisting of melamine, melamine cyanurate, melamine isocyanurate, and derivatives thereof, and more preferably melamine cyanurate, which can particularly enhance the flame retardancy of the insulating sheet 5.

[0142] The amount of flame retardant added is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 3 to 10 parts by mass, per 100 parts by mass of resin. By keeping the amount of flame retardant added within this range, the effect of enhancing flame retardancy is fully exerted, and side effects such as a decrease in mechanical properties due to an excess of flame retardant can be suppressed.

[0143] The flame retardant is, for example, in particulate form. In this case, the average particle size of the flame retardant is preferably 0.01 μm to 10 μm, more preferably 0.05 μm to 5 μm, and even more preferably 0.2 μm to 2 μm. When the average particle size of the flame retardant is within the above range, the dispersibility of the flame retardant is particularly good, thereby particularly improving the flame retardancy of the insulating sheet 5. The average particle size of the flame retardant is the particle size measured using a laser diffraction particle size distribution analyzer, where the cumulative total from the small diameter side in the volume-based particle size distribution is 50%.

[0144] Furthermore, the total amount of additives other than the flame retardant is preferably 0.1 parts by mass or more and 10 parts by mass or less, more preferably 0.3 parts by mass or more and 5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 3 parts by mass or less, relative to 100 parts by mass of the resin.

[0145] 1.3.3.Multilayer structure Next, an insulating sheet 5 according to a modification of the first embodiment will be described.

[0146] FIG. 4 is a cross-sectional view showing an insulating sheet 5 according to a modified example of the first embodiment. The insulating sheet 5 according to the modified example will be described below, but the following description will focus on the differences from the insulating sheet 5 shown in FIG. 3, and a description of similar points will be omitted.

[0147] The insulating sheet 5 shown in FIG. 4 is similar to the insulating sheet 5 shown in FIG. 3 except that it has a multi-layer structure.

[0148] The insulating sheet 5 shown in FIG. 4 has a first layer 501, an intermediate layer 503, and a second layer 502 laminated in this order from the bottom. Intermediate layer 503 preferably contains, in particular, an aromatic polycarbonate resin and a flame retardant. First layer 501 is laminated on the lower surface of intermediate layer 503 and contains a first resin. Second layer 502 is laminated on the upper surface of intermediate layer 503 and contains a second resin. The first resin and second resin are preferably materials having higher tracking resistance than the aromatic polycarbonate resin contained in intermediate layer 503.

[0149] According to this configuration, the aromatic polycarbonate resin is a polycarbonate resin containing an aromatic ring structure in the main chain, and the high ratio of the aromatic ring structure imparts good heat resistance to the intermediate layer 503. Furthermore, since the intermediate layer 503 contains a flame retardant, the intermediate layer 503 has good flame retardancy.

[0150] Furthermore, the intermediate layer 503 is sandwiched between the first layer 501 and the second layer 502. Therefore, even if creeping discharge occurs on the insulating sheet 5, the intermediate layer 503 is prevented from being directly exposed to corona discharge or the like. By using a material with higher tracking resistance than aromatic polycarbonate resin as the resin contained in the first layer 501 and the second layer 502, the insulating sheet 5 is endowed with good tracking resistance. Therefore, the insulating sheet 5 has excellent flame retardancy and tracking resistance.

[0151] Examples of methods for manufacturing the insulating sheet 5 shown in FIG. 4 include co-extrusion, dry lamination, extrusion lamination, and hot melt.

[0152] 1.3.4. Characteristics of Insulation Sheets Next, the characteristics of the insulating sheet 5 will be described.

[0153] 1.3.4.1. Tracking resistance The tracking resistance of the insulating sheet 5 can be quantified by the comparative tracking index CTI, which is an index of tracking resistance measured in accordance with ASTM D3638.

[0154] The comparative tracking index CTI (CTI value) of the insulating sheet 5 is preferably 600 V or more. If the CTI value is within this range, the rank PLC, which indicates tracking resistance, will be the highest rank of 0. Therefore, it can be said that an insulating sheet 5 having a CTI value within this range has particularly good tracking resistance.

[0155] The measurement method specified in IEC 60112, 3rd Edition, measures the CTI value using a 0.1% by mass aqueous solution of ammonium chloride and a platinum electrode. More specifically, the ammonium chloride aqueous solution is dropped a specified number of times (50 drops) and the voltage at which none of the test pieces (n=5) breaks down is determined, and this is taken as the CTI value.

[0156] The test piece used is an insulating sheet 5 having a thickness of 3 mm or more. The test piece may be one in which a plurality of insulating sheets 5 are stacked.

[0157] The methods for measuring the comparative tracking index CTI of resin materials and the comparative tracking index CTI of aromatic polycarbonate resins are the same as those described above. In this case, test pieces are sheets of these resins obtained by extrusion molding and having a thickness of 3 mm or more.

[0158] 1.3.4.2.Flame retardancy The flame retardancy of the insulating sheet 5 can be quantified by the flame retardancy rank determined in accordance with the UL94 standard (rank determined by the UL94V test or UL94VTM test).

[0159] The flame retardancy of the insulating sheet 5 is preferably such that the UL94V test rank is V-0 for a test piece having a thickness of 0.4 mm or more, or the UL94VTM test rank is VTM-0 for a test piece having a thickness of 0.4 mm or more.

[0160] An insulating sheet 5 that satisfies such a judgment rank satisfies the highest rank in each test, and therefore can be said to have particularly good flame retardancy.

[0161] In the UL94V test, a vertical combustion test is conducted using a test piece measuring 125±5mm x 13.0±0.5mm and having a thickness of 0.4mm or more and less than 13mm.

[0162] The UL94VTM test is conducted when the test specimen is too thin to be subjected to the UL94V test. The UL94VTM test is a vertical flame test using a test specimen measuring 200mm x 50mm and with a thickness of 0.025mm or more but less than 0.40mm.

[0163] 1.3.4.3.Breakdown voltage The breakdown voltage of insulating sheet 5 is a breakdown voltage measured in accordance with the method for measuring the strength of dielectric breakdown (AC test) specified in JIS C 2318:2020.

[0164] The breakdown voltage of the insulating sheet 5 is preferably 5 kV or higher, more preferably 7 kV to 60 kV, and even more preferably 10 kV to 50 kV. An insulating sheet 5 that satisfies such a breakdown voltage contributes to ensuring sufficient insulation even when the insulation clearance is short. Note that the breakdown voltage may exceed the upper limit, but is preferably equal to or lower than the upper limit in order to minimize individual differences.

[0165] 1.4.Method for manufacturing the insulating sheet fixing structure Next, a description will be given of a method for manufacturing the fixing structure of the insulating sheet according to the first embodiment. In the following description, a method for manufacturing the insulating sheet 5 according to the first embodiment will be described as an example.

[0166] Fig. 5 is a process diagram illustrating a method for manufacturing the insulating sheet fixing structure according to the first embodiment. Fig. 6 and Fig. 7 are partial cross-sectional views illustrating a method for manufacturing the insulating sheet fixing structure shown in Fig. 5.

[0167] The method for manufacturing the insulating sheet fixing structure 1 shown in FIG. 5 includes a convex molded portion forming step S100, a convex molded portion inserting step S102, and an extension portion forming step S104.

[0168] 1.4.1. Convex molded part forming process In the convex molded portion forming step S100, first, a molded sheet 50 having a flat plate portion 52 and a convex molded portion 58 is prepared. This molded sheet 50 is obtained by performing secondary processing on a flat plate sheet that serves as an original roll, thereby providing the convex molded portion 58 that is formed to protrude from the flat plate portion 52. Note that the convex molded portion 58 may have holes that penetrate through it in the thickness direction, but is preferably a shape without holes (a shape with a bottom). This makes it possible to suppress a decrease in the mechanical strength of the convex molded portion 58 and the extension portions 54 and connecting portions 56, which will be described later and are obtained by thermoforming the convex molded portion 58.

[0169] The method for producing the flat sheet is not particularly limited, but examples thereof include methods for forming a sheet from raw materials, such as calendaring, extrusion, pressing, and casting.

[0170] Next, the flat sheet is subjected to secondary processing. As a result, flat portions 52 and convex molded portions 58 are formed in the flat sheet, and the molded sheet 50 shown in FIG. 6(a) is obtained. Examples of secondary processing include thermoforming, folding, punching, cutting, etc. Among these, thermoforming includes vacuum forming, pressure forming, vacuum pressure forming, etc. Note that the manufacturing method of molded sheet 50 is not limited to the above method.

[0171] 1.4.2. Convex molding part insertion process In the convex molded portion insertion step S102, a lid portion 22 is prepared that is insulated and protected by an insulating sheet 5. Then, as shown in FIG. 6(a), a convex molded portion 58 is inserted into the through-hole 224 from the first surface 231 side of the lid portion 22. Then, as shown in FIG. 6(b), the tip of the convex molded portion 58 is caused to protrude toward the second surface 232 side of the lid portion 22.

[0172] The cross-sectional shape of the convex molded portion 58 in the XZ plane is not particularly limited, but may be a shape in which the outer diameter decreases upward, as shown in FIG. 6(a). This allows the above-mentioned insertion operation to be performed efficiently. Furthermore, the convex molded portion 58 having such a cross-sectional shape also contributes to improving the demolding efficiency during thermoforming. Furthermore, such a cross-sectional shape can suppress residual stress generated in the convex molded portion 58 and prevent warping, cracking, and the like. Note that, if the outer shape of the XY cross section of the convex molded portion 58 is a circle, the outer diameter refers to the diameter of the circle. Furthermore, if the outer shape of the XY cross section of the convex molded portion 58 is a shape other than a circle, the outer diameter refers to the diameter of the circumscribing circle of that shape.

[0173] 1.4.3. Extension section formation process In the extension portion forming step S104, first, as shown in FIG. 7(c), a hot plate 6 is pressed from above against the tip of the convex formed portion 58. Then, the hot plate 6 is lowered while heating the tip of the convex formed portion 58. This performs a thermoforming process by rolling the tip. As a result, as shown in FIG. 7(d), the tip of the convex formed portion 58 can be expanded along the XY plane, and the extension portion 54 is obtained.

[0174] Furthermore, when formed using the above method, a portion of the extension portion 54 may enter the through-hole 224, as shown in FIG. 7(d). In FIG. 7(d), the portion that enters the through-hole 224 is referred to as a "press-fit portion 542." By providing the press-fit portion 542, the insulating sheet 5 can be fixed more securely. This prevents the insulating sheet 5 from rattling even when subjected to vibrations, etc., thereby suppressing the generation of abnormal noise, dust, etc. Note that the press-fit portion 542 may be provided as needed and may be omitted.

[0175] The heating temperature when thermoforming the tip of the convex molded portion 58 is not particularly limited, but is preferably 130°C or higher and 260°C or lower, and more preferably 140°C or higher and 240°C or lower. This allows thermoforming into the desired shape without melting or excessive softening. Furthermore, since the thickness of the extension portion 54 can be prevented from becoming too thin or too thick, the extension portion 54 and connecting portion 56 have good mechanical strength.

[0176] The hot plate 6 is not particularly limited as long as it is a member that can heat the convex molding portion 58 to the above temperature. The lower surface of the hot plate 6 may be flat or may have a predetermined shape. For example, by providing the hot plate 6 with a molding surface having a cavity corresponding to the shape of the extension portion 54 to be formed, the extension portion 54 of the desired shape can be formed.

[0177] According to the above method, the insulating sheet fixing structure 1, which has a small number of parts and is resistant to deterioration of fixing strength due to heat, vibration, etc., can be easily manufactured with a small number of assembly steps.

[0178] 2. Second embodiment Next, a mounting board and an insulating sheet fixed to the mounting board will be described as a fixing structure for an insulating sheet according to a second embodiment.

[0179] FIG. 8 is a cross-sectional view showing an insulating sheet 5 and a mounting substrate 9 (object to be protected) to which an insulating sheet fixing structure 1 according to the second embodiment is applied.

[0180] The second embodiment will be described below, focusing on the differences from the first embodiment and omitting a description of similarities. Note that in Fig. 8, the same reference numerals are used to designate the same components as those in the first embodiment.

[0181] The second embodiment is similar to the first embodiment except that the object to which the insulating sheet 5 is fixed is different.

[0182] The insulating sheet 5 shown in Fig. 8 is fixed to a mounting substrate 9 (protected object), which is a voltage application portion. The insulating sheet 5 shown in Fig. 8 has a flat portion 52, an extension portion 54, and a connecting portion 56, similar to the first embodiment.

[0183] As in the first embodiment, the mounting board 9 includes a wiring board 90 (base), a power semiconductor element 91, and a bus bar 92, and is insulated and protected by an insulating sheet 5. Because a high voltage is applied to the power semiconductor element 91 and the bus bar 92, ensuring insulation by the insulating sheet 5 is useful. This improves the withstand voltage and reduces the probability of discharge, achieving the same effect as increasing the spatial distance between the mounting board 9, which is the voltage application section, and other components. Therefore, use of the insulating sheet 5 reduces dead space in a device including the mounting board 9 and increases the degree of freedom in arranging other components, while also achieving a high withstand voltage and improving electrical reliability, and enabling a device including the mounting board 9 to be made smaller and thinner without sacrificing electrical reliability.

[0184] Furthermore, a through hole 93 is formed in the wiring substrate 90. Similar to the through hole 224 in the first embodiment, this through hole 93 functions as a fixing means for fixing the insulating sheet 5 together with the extension portion 54 and the connecting portion 56.

[0185] The flat portion 52 of the insulating sheet 5 extends in a flat plate shape along the upper surface 901 (first surface) of the wiring board 90. This makes it possible to sufficiently reduce the number of electrical paths between the mounting board 9 and other components, thereby sufficiently improving insulation.

[0186] Furthermore, the connecting portion 56 is disposed within the through-hole 93, and the extension portion 54 extends outside the through-hole 93 on the lower surface 902 (second surface) of the wiring board 90. This prevents the extension portion 54 from being pulled into the through-hole 93 even when a tensile load is applied. This effect is also well maintained even in an environment where heat, vibration, etc. are applied. This makes it possible to realize an insulating sheet fixing structure 1 in which the fixing force is less likely to decrease even in such an environment.

[0187] Furthermore, the insulating sheet 5 shown in FIG. 8 has component insertion portions 582 and 584. The component insertion portions 582 and 584 are each formed to protrude upward from the flat plate portion 52. A space into which a component can be inserted is formed on the lower surface of the component insertion portions 582 and 584. Specifically, a power semiconductor element 91 is inserted on the lower surface of the component insertion portion 582 shown in FIG. 8. Furthermore, a bus bar 92 is inserted on the lower surface of the component insertion portion 584. By forming the insulating sheet 5 so that it conforms to the voltage application portion in this way, the probability of occurrence of creeping discharge, spatial discharge, and the like can be further reduced. In the second embodiment as described above, the same effects as in the first embodiment can be obtained.

[0188] 3. Third embodiment Next, a busbar structure and an insulating sheet fixed to the busbar structure will be described as an insulating sheet fixing structure according to a third embodiment.

[0189] Fig. 9 is a plan view showing an insulating sheet 5 and a bus bar structure 3 (protected object) to which an insulating sheet fixing structure 1 according to the third embodiment is applied. Fig. 10 is a cross-sectional view of the insulating sheet fixing structure 1 shown in Fig. 9 taken along line AA.

[0190] The third embodiment will be described below, focusing on the differences from the first embodiment, and a description of similarities will be omitted. Note that in Figures 9 and 10, the same components as those in the first embodiment are denoted by the same reference numerals.

[0191] The third embodiment is similar to the first embodiment except that the object to which the insulating sheet 5 is fixed is different.

[0192] The insulating sheet 5 shown in Fig. 9 is fixed to the bus bar structure 3 (protected body), which is a voltage application part. The insulating sheet 5 shown in Fig. 9 has a flat portion 52, an extension portion 54, and a connecting portion 56, similar to the first embodiment.

[0193] The busbar structure 3 is a conductor that connects a circuit board (not shown) to a power source, and is insulated and protected by the insulating sheet 5. Since a high voltage is applied to the busbar structure 3, ensuring insulation by the insulating sheet 5 is useful.

[0194] The busbar structure 3 shown in Fig. 9 has busbar 31 and busbar 32, which have currents flowing in opposite directions. As shown in Figs. 9 and 10, busbar 31 and busbar 32 are each made of a metal plate. Furthermore, as shown in Figs. 9 and 10, busbar 31 and busbar 32 partially overlap each other in the thickness direction. An insulating sheet 5 is disposed between busbar 31 and busbar 32.

[0195] The bus bar 31 has a flat base 312. The base 312 has a through hole 314 formed therein. Similar to the through hole 224 of the first embodiment, the through hole 314 functions as a fixing means for fixing the insulating sheet 5 together with the extension portion 54 and the connecting portion 56. The flat portion 52 of the insulating sheet 5 extends along the lower surface 315 (first surface) of the base 312. This ensures insulation between the bus bar 31 and the bus bar 32.

[0196] Furthermore, the connecting portion 56 is disposed within the through-hole 314, and the extension portion 54 extends outward from the through-hole 314 on the upper surface 316 (second surface) of the base 312. This prevents the extension portion 54 from being pulled into the through-hole 314 even when a tensile load is applied. This effect is also maintained favorably in environments where heat, vibration, etc. are present. This makes it possible to realize an insulating sheet fixing structure 1 in which the fixing force is unlikely to decrease even in such environments.

[0197] 9 and 10 further includes a wall portion 586. The wall portion 586 is a bent portion that protrudes upward from the flat plate portion 52. As shown in FIG. 10, the wall portion 586 is disposed so as to cover the side surface of the bus bar 31. This allows a longer creepage insulation distance to be secured between the bus bar 31 and the bus bar 32 compared to when the wall portion 586 is not present.

[0198] Furthermore, flat portion 52 of insulating sheet 5 extends in a flat plate shape along the space between busbar 31 and busbar 32. This ensures reliable insulation between busbar 31 and busbar 32. Furthermore, because flat portion 52 has sufficient insulation properties even though it is thin, the distance between busbar 31 and busbar 32 can be sufficiently reduced. This allows the magnetic flux generated by the current flowing through busbar 31 and the magnetic flux generated by the current flowing through busbar 32 to cancel each other out, reducing the inductance component.

[0199] From the above, by using insulating sheet 5, it is possible to increase the withstand voltage between busbars 31 and 32, thereby improving electrical reliability, and since it is easy to shorten the distance between busbars 31 and 32, it is possible to reduce the inductance component and reduce surge voltage in busbar structure 3. In the third embodiment as described above, the same effects as in the first embodiment can be obtained.

[0200] 4. Effects of the above embodiment The insulating sheet fixing structure 1 according to the embodiment includes an insulating sheet 5 and an object to be protected (such as a housing 20, a mounting board 9, or a busbar structure 3). The insulating sheet 5 is made of a resin material. The object to be protected fixes the insulating sheet 5 and is insulated and protected by the insulating sheet 5. The object to be protected has a base and a through hole. The base has a first surface and a second surface that are opposite surfaces. The through hole penetrates the base from the first surface to the second surface.

[0201] The insulating sheet 5 also has a flat portion 52, an expanding portion 54, and a connecting portion 56. The flat portion 52 extends in a flat plate shape along the first surface. The expanding portion 54 is located outside the through-hole in the second surface. The connecting portion 56 connects the flat portion 52 and the expanding portion 54, and is inserted into the through-hole.

[0202] With this configuration, the fixing force is generated by the shape of the insulating sheet 5 itself, which reduces the number of parts and therefore the assembly man-hours. Furthermore, with the above configuration, the fixing force is less likely to decrease because it is less susceptible to the effects of heat and vibration.

[0203] In the insulating sheet fixing structure 1 according to the embodiment, the extension portion 54 and the connecting portion 56 are thermoformed portions.

[0204] With this configuration, the constituent materials are continuous at the boundary between the flat plate portion 52 and the connecting portion 56, and at the boundary between the connecting portion 56 and the expanding portion 54, ensuring integrity. This makes it easier to prevent breakage and the like from occurring even when a load is applied to the insulating sheet 5.

[0205] In the insulating sheet fixing structure 1 according to the embodiment, the insulating sheet 5 does not have any holes penetrating in the thickness direction.

[0206] This configuration increases the mechanical strength of the insulating sheet 5. In particular, by not providing holes penetrating the extended portion 54, the mechanical strength of the extended portion 54 can be increased. As a result, an insulating sheet 5 with particularly high fixing strength can be obtained.

[0207] In the insulating sheet fixing structure 1 according to the embodiment, when the second surface of the base is viewed in plan, the extension portion 54 expands so as to surround the through-hole. With this configuration, the fixing force of the extension portion 54 to the insulating sheet 5 can be particularly increased.

[0208] In the insulating sheet fixing structure 1 according to the embodiment, the width W of the expansion portion 54 in the radial direction of the through hole is 0.5 mm or more.

[0209] With this configuration, the expansion portion 54 can more reliably function as a stopper.

[0210] In the insulating sheet fixing structure 1 according to the embodiment, the thickness of the insulating sheet 5 is not less than 0.02 mm and not more than 1.50 mm.

[0211] This configuration provides an insulating sheet 5 that is excellent in flame retardancy, tracking resistance, and insulating properties. Furthermore, when the extensions 54 and the connecting portions 56 are formed by thermoforming, they can be formed easily and in a short time.

[0212] In the insulating sheet fixing structure 1 according to the embodiment, the object to be protected is the housing 20 that houses the voltage application unit to which a voltage is applied.

[0213] With this configuration, it is possible to achieve high voltage resistance and improved electrical reliability without increasing the size of the housing 20, and it is possible to make the housing 20 smaller and thinner without compromising electrical reliability.

[0214] In the insulating sheet fixing structure 1 according to the embodiment, the object to be protected is the mounting board 9. Such a configuration reduces dead space in a device that includes the mounting substrate 9, increases the degree of freedom in arranging other components, and also enables a higher voltage resistance and improved electrical reliability, as well as making the device that includes the mounting substrate 9 smaller and thinner without impairing electrical reliability.

[0215] In the insulating sheet fixing structure 1 according to the embodiment, the object to be protected is the bus bar structure 3.

[0216] According to this configuration, the busbar structure 3 can be made to withstand a high voltage, and electrical reliability can be improved, and the inductance component can be reduced, thereby reducing surge voltage.

[0217] In the insulating sheet fixing structure 1 according to the embodiment, the insulating sheet 5 is made mainly of a thermoplastic resin.

[0218] According to this configuration, since the thermoplastic resin can be plastically deformed by heat and has excellent secondary processability, the insulating sheet 5 can be manufactured by thermoforming and has excellent manufacturability.

[0219] In the insulating sheet fixing structure 1 according to the embodiment, the thermoplastic resin is an aromatic polycarbonate resin or a polymer alloy containing aromatic polycarbonate.

[0220] This configuration provides an insulating sheet 5 that has excellent heat resistance and flame retardancy due to the aromatic ring structure. In addition, the insulating sheet 5 has other properties due to the compatible resin that is alloyed with the aromatic polycarbonate resin.

[0221] In the insulating sheet fixing structure 1 according to the embodiment, the insulating sheet 5 contains a flame retardant made of a nitrogen-containing compound.

[0222] This configuration can further improve the flame retardancy of the insulating sheet 5. Furthermore, since the nitrogen-containing compound does not contain halogen atoms, a so-called halogen-free and fluorine-free insulating sheet 5 can be realized.

[0223] The manufacturing method of the fixing structure for an insulating sheet according to the embodiment is a method for manufacturing the fixing structure 1 for an insulating sheet, and includes a convex molded portion inserting step S102 and an extension portion forming step S104. In the convex molded portion inserting step S102, a molded sheet 50 having a flat plate portion 52 and a convex molded portion 58 formed to protrude from the flat plate portion 52 is prepared, and the convex molded portion 58 is inserted into the through hole 224 from the first surface 231 side, causing the tip of the convex molded portion 58 to protrude toward the second surface 232 side. In the extension portion forming step S104, the tip of the convex molded portion 58 is thermoformed to expand, thereby forming the extension portion 54.

[0224] With this configuration, the number of parts and assembly steps are reduced, and the insulating sheet fixing structure 1 that is less susceptible to deterioration in fixing force due to heat, vibration, etc. can be easily manufactured.

[0225] Although the fixing structure for an insulating sheet and the method for manufacturing the fixing structure for an insulating sheet of the present invention have been described above, the present invention is not limited to the above-described embodiment.

[0226] For example, the insulating sheet provided in the insulating sheet fixing structure of the present invention may contain an additive other than the additive described in the above embodiment.

[0227] Furthermore, the insulating sheet provided in the insulating sheet fixing structure of the present invention may have a layer having any function added to the layer configuration described in the above embodiment, such as an adhesive layer, a bonding layer, a protective layer, a release layer, etc.

[0228] Furthermore, the method for manufacturing the insulating sheet fixing structure of the present invention may be such that any desired step is added to the above-described embodiment. [Example]

[0229] Next, specific examples of the present invention will be described, but the present invention is not limited to the descriptions of these examples.

[0230] 5. Preparation of Test Specimens for Insulation Sheets In order to evaluate the performance of the polymer alloy obtained by alloying the above-mentioned aromatic polycarbonate resin (PC resin) with a compatible resin as a material for an insulating sheet, a test piece for the insulating sheet was prepared as follows.

[0231] First, the materials shown in Table 2 were mixed in the compounding ratios shown in Tables 3 to 6, and then melted and kneaded in a twin-screw extruder to prepare pelletized flame-retardant resin compositions. The produced flame-retardant resin compositions were extruded into sheets using a counter-rotating twin-screw extruder and a T-die, etc., to prepare test pieces for insulating sheets having the layer structures and thicknesses shown in Tables 3 to 6.

[0232] Table 2 shows the attributes of each material, such as the compound name, viscosity average molecular weight, tracking resistance (CTI value), glass transition temperature, average particle size, etc.

[0233] The compatible resin b1 shown in Table 2 is a heat-resistant polycarbonate resin derived from bisphenol A and bisphenol TMC. The content of structural units derived from bisphenol TMC in the compatible resin b1 is 60 mol %.

[0234] Furthermore, the compatible resin b2 shown in Table 2 is an aliphatic polycarbonate resin containing 60 mol % of carbonate units containing the diol residue represented by the formula (4).

[0235] [Table 2]

[0236] 6. Evaluation of test specimens for insulation sheets Next, the prepared test pieces for insulating sheets were evaluated for the following items.

[0237] 6.1.Flame retardancy The flame retardancy rank was determined for each insulating sheet test piece numbered as shown in Tables 3 to 6 through tests conducted in accordance with the aforementioned UL94 standard. The insulating sheet test pieces were used as they were for the test pieces used to evaluate flame retardancy. The thickness of the insulating sheet test pieces was the thickness of one layer shown in Tables 3 to 6. The results were evaluated in accordance with the following evaluation criteria. The evaluation results are shown in Tables 3 to 6.

[0238] A: Flame retardancy rating is V-0 or VTM-0 B: Flame retardancy rating is V-1 or V-2, or VTM-1 or VTM-2 C: Flame retardancy rating is less than V-2 or VTM-2

[0239] 6.2. Tracking resistance The CTI values ​​of the insulating sheet test pieces of each number shown in Tables 3 to 6 were measured using the tracking resistance evaluation test described above. The thickness of the test piece for evaluating tracking resistance was 3 mm or more, obtained by stacking the insulating sheet test pieces of a single layer thickness shown in Tables 3 to 6. The measured CTI values ​​were evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 3 to 6.

[0240] A: The CTI value is 600V or more (rank is PLC0) B: The CTI value is 400V or more and less than 600V (rank is PLC1) C: The CTI value is less than 400V (rank is PLC2 or lower)

[0241] 6.3.Carbonization due to tracking For each insulating sheet test piece shown in Tables 3 to 6, the above-mentioned tracking resistance evaluation test was carried out, and then the test site was visually observed. The observation results were then evaluated in accordance with the following evaluation criteria. The evaluation results are shown in Tables 3 to 6.

[0242] A: Little discoloration due to carbonization (good appearance) B: There is a little bit of coloring due to carbonization (appearance is a little poor) C: A lot of discoloration due to carbonization (poor appearance)

[0243] 6.4. Processability The test pieces for insulating sheets of each number shown in Tables 3 to 6 were subjected to bending as described below, and the appearance of the bending results was evaluated to evaluate the workability of the test pieces for insulating sheets.

[0244] [1] Cut the insulating sheet test piece into a roughly square test piece for workability evaluation, measuring 15 mm ± 1 mm in length in the MD direction and 15 mm ± 1 mm in length in the TD direction.

[0245] [2] The test piece is bent in the center, a 3 kg weight is placed on it, and after leaving it for 1 minute, the weight is removed.

[0246] [3] Open the test piece and visually observe the condition of the bent part and record it. [4] With the test piece open, place a 3 kg weight on it, leave it for 1 minute, and then remove the weight. [5] Visually inspect the condition of the bent part and record it.

[0247] [6] Repeat steps [2] to [5] above and count the number of repetitions until cracks or holes appear in the folded part.

[0248] [7] The number of repetitions was evaluated in accordance with the following evaluation criteria to evaluate the processability of the test piece for the insulating sheet. The evaluation results are shown in Tables 3 to 6.

[0249] A: No cracks or holes were observed even after 10 or more repeated tests. B: Either cracks or holes occurred after 5 to 9 cycles C: Either cracks or holes occurred after 4 or fewer cycles

[0250] [Table 3]

[0251] [Table 4]

[0252] [Table 5]

[0253] [Table 6]

[0254] From the results shown in Tables 3 to 6, the following was confirmed regarding the constituent materials of the insulating sheets. The insulating sheet test pieces (No. 1 to 20) containing a polymer alloy with an aromatic polycarbonate resin and a compatible resin had better flame retardancy and tracking resistance than the insulating sheet test pieces (No. 21 to 26) that did not contain these.

[0255] -It was found that flame retardancy can be easily improved when polycarbonate resin is used as a compatible resin.

[0256] It was found that when a resin with a low ratio of aromatic rings was used as the compatible resin (compatible resins b3 and b4), or when a resin with a high glass transition temperature (compatible resin b1) was used, carbonization due to tracking was easily suppressed. [Explanation of symbols]

[0257] 1. Insulation sheet fixing structure 3 Busbar structure 5. Insulation sheet 6 hot plate 9 Mounting board 20 Case 21 Housing 22 Lid 31 Busbar 32 Busbar 50 Molded Sheet 52 Flat plate part 54 Extension 56 Connecting part 58 Convex molding part 90 Wiring board 91 Power semiconductor elements 92 Busbar 93 Through Hole 222 Base 224 Through hole 231 Page 1 232 2nd page 312 Base 314 Through hole 315 Bottom surface 316 Top surface 501 1st layer 502 2nd layer 503 Middle Class 542 Press-fit part 582 Component insertion part 584 Component insertion part 586 Wall 901 Top surface 902 Bottom surface S102 Convex molding part insertion process S104 Expansion section forming process

Claims

1. an insulating sheet made of a resin material; a protected object to which the insulating sheet is fixed and which is insulated and protected by the insulating sheet; Equipped with the object to be protected includes a substrate having a first surface and a second surface that are opposite surfaces to each other, and a through-hole that penetrates the substrate from the first surface to the second surface; The insulating sheet fixing structure is characterized in that the insulating sheet has a flat portion that extends flat along the first surface, an extension portion that is located outside the through hole on the second surface, and a connecting portion that connects the flat portion and the extension portion and is inserted into the through hole.

2. The insulating sheet fixing structure according to claim 1 , wherein the extension portion and the connecting portion are thermoformed portions.

3. 3. The insulating sheet fixing structure according to claim 1, wherein the insulating sheet does not have a hole penetrating in the thickness direction.

4. The insulating sheet fixing structure according to claim 1 or 2, wherein the extension portion extends so as to surround the through hole when the second surface is viewed in plan.

5. The insulating sheet fixing structure according to claim 4 , wherein the width of the expanded portion in the radial direction of the through hole is 0.5 mm or more.

6. 3. The insulating sheet fixing structure according to claim 1, wherein the insulating sheet has a thickness of 0.02 mm or more and 1.50 mm or less.

7. 3. The insulating sheet fixing structure according to claim 1, wherein the object to be protected is a housing that houses a voltage application unit to which a voltage is applied.

8. 3. The insulating sheet fixing structure according to claim 1, wherein the object to be protected is a mounting board.

9. 3. The insulating sheet fixing structure according to claim 1, wherein the object to be protected is a bus bar structure.

10. 3. The insulating sheet fixing structure according to claim 1, wherein the insulating sheet is made primarily of a thermoplastic resin.

11. The insulating sheet fixing structure according to claim 10 , wherein the thermoplastic resin is an aromatic polycarbonate resin or a polymer alloy containing aromatic polycarbonate.

12. 3. The insulating sheet fixing structure according to claim 1, wherein the insulating sheet contains a flame retardant made of a nitrogen-containing compound.

13. A method for manufacturing the insulating sheet fixing structure according to claim 1, comprising: a step of preparing a molded sheet having the flat plate portion and a convex molded portion molded so as to protrude from the flat plate portion, inserting the convex molded portion into the through hole from the first surface side, and causing a tip end of the convex molded portion to protrude to the second surface side; a step of performing a thermoforming process so as to expand the tip of the convex molded portion, thereby forming the expanded portion; 10. A method for manufacturing an insulating sheet fixing structure, comprising:

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